1. Field of the Invention
The present invention relates to a water base ink for ink-jet recording to be used for an ink-jet recording apparatus and an ink-jet recording apparatus which accommodates the same.
2. Related Art
In the ink-jet recording system, ink droplets are formed by using an ink discharge method including, for example, the electrostatic attraction method, the method in which mechanical vibration or displacement is applied to the ink by using a piezoelectric element or the like, and the method in which bubbles are generated by heating the ink to utilize the pressure generated thereby, and all or a part of the ink droplets are adhered to an objective recording material such as paper to perform the recording.
Those used as the ink for ink-jet recording to be used for the ink-jet recording system as described above include those obtained by dissolving or dispersing a water-soluble dye or a pigment in water or a liquid medium composed of water and a water-soluble organic solvent. In order to perform the recording in a well-suited manner for a long period of time by effecting the stable discharge without causing any clog-up at the nozzle and the orifice of the ink-jet printer, for example, the water base ink for ink-jet recording is required to have the following features. That is, the physical property values of the viscosity, the surface tension, and the density are appropriate values, neither appearance of any deposit nor change of the physical property value is caused, and the recorded image is excellent in water resistance and light resistance.
However, the conventional water base ink for ink-jet recording involved the following problem. That is, when a new ink cartridge is installed to the ink-jet printer to start the printing, then the ink cannot smoothly enter the narrow ink flow passage of the recording head, and any discharge defect such as discharge failure may be caused in some cases. Therefore, in order to perform the recording in a well-suited manner by avoiding, for example, the discharge failure at the recording head nozzle of the ink-jet printer, it has been necessary that the wettability of the ink in the recording head nozzle is improved to improve the performance of initial introduction into the recording head.
In order to obtain a good printing quality without any ink blur when the recording is performed with the ink-jet printer, the exclusive ink-jet paper is used. However, in recent years, it is more demanded to perform the recording on the regular paper rather than on the exclusive ink-jet paper, in view of the running cost and the consideration of the environment. Further, in the market of the ink-jet printer directed to home use and office use, the color ink-jet printer is overwhelmingly demanded as compared with the monochrome ink-jet printer. Nowadays, the color ink-jet printer is ordinary and normal. In contrast to such a situation, the conventional water base ink for ink-jet recording has involved such a problem that the printing quality is not sufficient when the recording is performed on the regular paper.
The principal factors of the insufficient printing quality on the regular paper may be pointed out as follows. Firstly, there is the feathering in which the ink is spread nonuniformly along the surface of the recording paper when the ink is permeated into the recording paper, and the edge of the image portion is notched, resulting in the failure to obtain any sharp edge of the image portion. Secondly, there is the color bleed in which the inks are mixed with each other at the portion (hereinafter referred to as “boundary” as well) at which the inks of different colors are adjoined, and the both inks are blurred, resulting in the deterioration of the printing quality.
Many techniques have been hitherto used in order to improve the performance of initial introduction into the recording head and avoid the feathering and the color bleed. In order to improve the performance of initial introduction into the recording head, for example, a method has been used generally and widely, in which the surface tension is lowered to an optimum value by adding an appropriate amount of surfactant to improve the wettability in the recording head. However, the ink, which is obtained by this method, has involved the following problems. That is, the surface tension is lowered, the wettability on the recording paper is raised as well, and the feathering is apt to occur.
In order to avoid the feathering, a method has been used generally and widely, in which the surface tension is raised. Specifically, for example, Japanese Patent Application Laid-open No. 8-259864 discloses a technique in which the permeation of the ink along the surface of the recording paper is suppressed to avoid the feathering by allowing the surface tension of the ink to be not less than 40 mN/m. However, the ink, which is obtained by this method, has involved the following problems. That is, the wettability on the recording paper is deteriorated, and the color bleed is caused in some cases. The drying performance of the ink on the recording paper is deteriorated, and the performance of initial introduction into the recording head is deteriorated in other cases.
In order to avoid the color bleed, those which have been used generally and widely include a method in which alkyl ether of polyvalent alcohol such as diethylene glycol monobutyl ether is blended as a permeating agent, and a method in which a surfactant is blended. Specifically, for example, Japanese Patent Application Laid-open No. 8-283631 discloses a technique in which a permeating agent and a surfactant are added into an ink to lower the surface tension so that the permeability into the paper is enhanced to avoid the color bleed. However, the ink, which is obtained by this method, has involved such a problem that it is impossible to suppress the feathering.
As described above, the conventional water base inks for ink-jet recording have involved such problems that it is impossible to realize both of the improvement in performance of initial introduction into the recording head and the improvement in printing quality to be brought about by avoiding the feathering and the color bleed, and it is impossible to obtain any sufficient printing quality.